​Seasonal affective disorder (SAD) is a type of depression that comes and goes in a seasonal pattern.SAD is sometimes known as "winter depression" because the symptoms are usually more apparent and more severe during the winter.A few people with SAD may have symptoms during the summer and feel better during the winter.Symptoms of SAD Symptoms of SAD can include:

a persistent low mood

a loss of pleasure or interest in normal everyday activities

irritability

feelings of despair, guilt and worthlessness

feeling lethargic (lacking in energy) and sleepy during the day

sleeping for longer than normal and finding it hard to get up in the morning

For some people, these symptoms can be severe and have a significant impact on their day-to-day activities.Read more about the symptoms of SAD.When to see your GP You should consider seeing your GP if you think you might have SAD and you're struggling to cope.Your GP can carry out an assessment to check your mental health. They may ask you about your mood, lifestyle, eating habits and sleeping patterns, plus any seasonal changes in your thoughts and behaviour.Read more about diagnosing SAD.What causes SAD? The exact cause of SAD isn't fully understood, but it's often linked to reduced exposure to sunlight during the shorter autumn and winter days.The main theory is that a lack of sunlight might stop a part of the brain called the hypothalamus working properly, which may affect the:

production of melatonin – melatonin is a hormone that makes you feel sleepy; in people with SAD, the body may produce it in higher than normal levels

production of serotonin – serotonin is a hormone that affects your mood, appetite and sleep; a lack of sunlight may lead to lower serotonin levels, which is linked to feelings of depression

body's internal clock (circadian rhythm) – your body uses sunlight to time various important functions, such as when you wake up, so lower light levels during the winter may disrupt your body clock and lead to symptoms of SAD

It's also possible that some people are more vulnerable to SAD as a result of their genes, as some cases appear to run in families.Treatments for SAD range of treatments are available for SAD. Your GP will recommend the most suitable treatment programme for you.The main treatments are:

The symptoms of seasonal affective disorder (SAD) are similar to those of normal depression, but they occur repetitively at a particular time of year.They usually start in the autumn or winter and improve in the spring.The nature and severity of SAD varies from person to person. Some people just find the condition a bit irritating, while for others it can be severe and have a significant impact on their day-to-day life.Depression Signs that you may be depressed include:

a persistent low mood

a loss of pleasure or interest in normal everyday activities

feeling irritable

feelings of despair, guilt and worthlessness

low self-esteem

tearfulness

feeling stressed or anxious

a reduced sex drive

becoming less sociable

A small number of people will experience these symptoms in phases that are separated by "manic" periods where they feel happy, energetic and much more sociable.Other symptomsIn addition to symptoms of depression, you may also:

be less active than normal

feel lethargic (lacking in energy) and sleepy during the day

sleep for longer than normal and find it hard to get up in the morning

find it difficult to concentrate

have an increased appetite – some people have a particular craving for foods containing lots of carbohydrates and end up gaining weight as a result

These symptoms may make everyday activities increasingly difficult.When to see your GP You should see your GP if you think you might have SAD and you're finding it difficult to cope.There are a number of helpful treatments your GP may be able to recommend.​

Visit your GP if you have symptoms of seasonal affective disorder (SAD). Effective treatments are available if you're diagnosed with the condition.Your GP may carry out a psychological assessment to check your mental health. They may ask about:

your mood

your lifestyle

your eating and sleeping patterns

any seasonal changes in your thoughts and behaviour

whether your symptoms prevent you from carrying out normal activities

whether there's anything in your personal or family history that may contribute to a depressive disorder, such as a family history of depression

Your GP may also carry out a brief physical examination.Confirming a diagnosis of SAD SAD can be difficult to diagnose because there are many other types of depression that have similar symptoms.It may therefore take some time before you and your GP realise that your symptoms are forming a regular pattern.A diagnosis of SAD can usually be confirmed if:

A number of treatments are available for seasonal affective disorder (SAD), including cognitive behavioural therapy, antidepressants and light therapy.Your GP will recommend the most suitable treatment option for you, based on the nature and severity of your symptoms. This may involve using a combination of treatments to get the best results.NICE recommendations The National Institute for Health and Care Excellence (NICE) recommends that SAD should be treated in the same way as other types of depression.This includes using talking treatments such as cognitive behavioural therapy (CBT) or medication such as antidepressants.Light therapy is also a popular treatment for SAD, although NICE says it's not clear whether it's effective.See NICE guidance about the treatment and management of depression in adults.Things you can try yourself There are a number of simple things you can try that may help improve your symptoms, including:

try to get as much natural sunlight as possible – even a brief lunchtime walk can be beneficial

if possible, avoid stressful situations and take steps to manage stress

It can also be helpful to talk to your family and friends about SAD, so they understand how your mood changes during the winter. This can help them to support you more effectively.Psychosocial treatments Psychosocial treatments focus on both psychological aspects (how your brain functions) and social aspects (how you interact with others).Cognitive behavioural therapy Cognitive behavioural therapy (CBT) is based on the idea that the way we think and behave affects the way we feel. Changing the way you think about situations and what you do about them can help you feel better.If you have CBT, you'll have a number of sessions with a specially trained therapist, usually over several weeks or months. Your programme could be:

an individual programme of self-help

a programme designed for you and your partner (if your depression is affecting your relationship)

a group programme that you complete with other people in a similar situation

a computer-based CBT programme tailored to your needs and supported by a trained therapist

Read more about CBT. Counselling and psychodynamic psychotherapy Counselling is another type of talking therapy that involves talking to a trained counsellor about your worries and problems.During psychodynamic psychotherapy you discuss how you feel about yourself and others and talk about experiences in your past. The aim of the sessions is to find out whether anything in your past is affecting how you feel today.It's not clear exactly how effective these 2 therapies are in treating depression.Read more about psychotherapy.Antidepressants are often prescribed to treat depression and are also sometimes used to treat severe cases of SAD, although the evidence to suggest they're effective in treating SAD is limited.Antidepressants are thought to be most effective if taken at the start of winter before symptoms appear, and continued until spring.Selective serotonin reuptake inhibitors (SSRIs) are the preferred type of antidepressant for treating SAD. They increase the level of the hormone serotonin in your brain, which can help lift your mood.If you're prescribed antidepressants, you should be aware that:

it can take up to 4 to 6 weeks for the medication to take full effect

you should take the medication as prescribed and continue taking it until advised to gradually stop by your doctor

some antidepressants have side effects and may interact with other types of medication you're taking

Common side effects of SSRIs include feeling agitated, shaky or anxious, an upset stomach and diarrhoea or constipation. Check the information leaflet that comes with your medication for a full list of possible side effects.Read more about antidepressants.Light therapy Some people with SAD find that light therapy can help improve their mood considerably. This involves sitting by a special lamp called a light box, usually for around 30 minutes to an hour each morning.Light boxes come in a variety of designs, including desk lamps and wall-mounted fixtures. They produce a very bright light. The intensity of the light is measured in lux – the higher lux, the brighter the light.Dawn-stimulating alarm clocks, which gradually light up your bedroom as you wake up, may also be useful for some people.The light produced by the light box simulates the sunlight that's missing during the darker winter months.It's thought the light may improve SAD by encouraging your brain to reduce the production of melatonin (a hormone that makes you sleepy) and increase the production of serotonin (a hormone that affects your mood).Who can use light therapy? Most people can use light therapy safely. The recommended light boxes have filters that remove harmful ultraviolet (UV) rays, so there's no risk of skin or eye damage for most people.However, exposure to very bright light may not be suitable if you:

have an eye condition or eye damage that makes your eyes particularly sensitive to light

are taking medication that increases your sensitivity to light, such as certain antibiotics and antipsychotics, or the herbal supplement St. John's Wort

Speak to your GP if you're unsure about the suitability of a particular product.Trying light therapy Light boxes aren't usually available on the NHS, so you'll need to buy one yourself if you want to try light therapy.Before using a light box, you should check the manufacturer's information and instructions regarding:

whether the product is suitable for treating SAD

the light intensity you should be using

the recommended length of time you need to use the light

Make sure that you choose a light box that is medically approved for the treatment of SAD and produced by a fully certified manufacturer.Does light therapy work? There's mixed evidence regarding the overall effectiveness of light therapy, but some studies have concluded it is effective, particularly if used first thing in the morning. It's thought that light therapy is best for producing short-term results. This means it may help relieve your symptoms when they occur, but you might still be affected by SAD next winter.When light therapy has been found to help, most people noticed an improvement in their symptoms within a week or so.Side effects of light therapy It's rare for people using light therapy to have side effects. However, some people may experience: